T cells play a pivotal role in the regulation of immune responses and are important for establishing immunity to pathogens. In addition, T cells are often activated during inflammatory autoimmune diseases, such as rheumatoid arthritis, inflammatory bowel disease, type I diabetes, multiple sclerosis, Sjogren's disease, myasthenia gravis, psoriasis, and lupus. T cell activation is also an important component of transplant rejection, allergic reactions, and asthma.
T cells are activated by specific antigens through the T cell receptor (TCR) which is expressed on the cell surface. This activation triggers a series of intracellular signaling cascades mediated by enzymes expressed within the cell (Kane, L P et al. Current Opinion in Immunol. 200, 12, 242). These cascades lead to gene regulation events that result in the production of cytokines, like interleukin-2 (IL-2). IL-2 is a critical cytokine in T cell activation, leading to proliferation and amplification of specific immune responses.
One class of enzymes shown to be important in signal transduction are the kinases. Members of the Src-family of tyrosine kinases include, for example: Lck, Fyn(B), Fyn(T), Lyn, Src, Yes, Hck, Fgr and Blk (for review see: Bolen, J B, and Brugge, J S Annu. Rev. Immunol 1997, 15, 371). Gene disruption studies suggest that inhibition of some members of the src family of kinases would potentially lead to therapeutic benefit. Src(−/−) mice have abnormalities in bone remodeling or osteopetrosis (Soriano, P. Cell 1991, 64, 693), suggesting that inhibition of this kinase might be useful in diseases of bone resorption, such as osteoporosis. Lck(−/−) mice have defects in T cell maturation and activation (Anderson, S J et al. Adv. Immunol. 1994, 56, 151), suggesting that inhibition of this kinase might be useful in diseases of T cell mediated inflammation. In addition, human patients have been identified with mutations effecting Lck kinase activity (Goldman, F D et al. J. Clin. Invest. 1998, 102, 421). These patients suffer from a severe combined immunodeficiency disorder (SCID).
Ack, a gene containing a tyrosine kinase domain, is also reported to possess tyrosine kinase activity, lending to the belief that it is involved in the regulatory mechanism that sustains the GTP-bound active form of cdc42Hs, which is directly linked to a tyrosine phosphorylation signal transduction pathway (Manser et. Al., Nature 363(6427), 364-367, 1994). More specifically, the activated p21cdc42Hs kinase gene encodes an intracellular, non-receptor tyrosine kinase that binds cdc42Hs in its GTP-bound form and inhibits the GTPase activity of p21cdc42, a Ras-like protein involved in cell growth. Accordingly, Ack is a target believed to be useful in the regulation of cancer.
Without wishing to imply that the compounds disclosed in the present invention possess pharmacological activity only by virtue of an effect on a single biological process, it is believed that the compounds modulate T cell activation by way of inhibition of one or more of the multiple protein tyrosine kinases involved in early signal transduction steps leading to T cell activation, for example by way of inhibition of Lck kinase.
Src-family kinases are also important for signaling downstream of other immune cell receptors. Fyn, like Lck, is involved in TCR signaling in T cells (Appleby, M W et al. Cell 1992, 70, 751). Hck and Fgr are involved in Fcγ receptor signaling leading to neutrophil activation (Vicentini, L. et al. J. Immunol. 2002, 168, 6446). Lyn and Src also participate in Fcγ receptor signaling leading to release of histamine and other allergic mediators (Turner, H. and Kinet, J-P Nature 1999, 402, B24). These findings suggest that Src family kinase inhibitors may be useful in treating allergic diseases and asthma.
Src kinases have also been found to be activated in tumors including sarcoma, melanoma, breast, and colon cancers suggesting that Src kinase inhibitors may be useful anti-cancer agents (Abram, C L and Courtneidge, S A Exp. Cell Res. 2000, 254, 1).
Src kinase inhibitors have also been reported to be effective in an animal model of cerebral ischemia (R. Paul et al. Nature Medicine 2001, 7, 222), suggesting that Src kinase inhibitors may be effective at limiting brain damage following stroke.
Several groups have published on inhibitors of Src family kinase and the activities of these inhibitors in various in vitro and in vivo biological systems. These include the 2-phenylamino-imidazo [4,5-h]isoquinolin-9-ones (Snow, R J et al. J. Med. Chem. 2002, 45, 3394), the pyrazolo [3,4-d]pyrimidines (Burchat, A F et al. Bioorganic and Med. Chem. Letters 2002, 12, 1687. Hanke, J H et al. J. Biol. Chem. 1996, 271, 695), the pyrrolo [2,3-d]pyrimidines (Altmann, E et al. Bioorganic and Med. Chem. Letters 2001, 11, 853), the anilinoquinazolines (Wang, Y D et al. Bioorganic and Med. Chem. Letters 2000, 10, 2477), and the imidazoquinoxalines (Chen, P. et al. Bioorganic and Med. Chem. Letters 2002, 12, 3153).